1. Field of the Invention
This invention relates in general to the field of telecommunications, and more particularly to an apparatus and method for providing T1/T1 telecommunications links over a high bandwidth data network.
2. Description of the Related Art
Along with the widespread proliferation of the telephone in the early 1900""s came the attendant development of the supporting infrastructure required to interconnect millions of these communication devices. A complex network of wires, cables, and switching equipment was developed to support the switching of calls from their source to their destination. To a significant degree, this infrastructure is still in place today.
The backbone of the public switched telephone network (PSTN) consists of a network of local exchanges, or local switches. A local switch is the point at which all of the telephones within a its local area connect into the PSTN. A switch is also referred to as a central office switch or a telecommunications switch. Each of the telephones in a local area are connected to a pair of telephone wires and all of the telephone wires in the local area originate at the central office switch. When a user picks up the receiver of his/her telephone, equipment within the local switch generates the dial tone that he/she hears in the receiver. When the user dials a destination number, the equipment in the local exchange decodes the number and routes the call to its destination. If the destination telephone is also connected to the local switch, or central office switch, then the equipment connects the calling telephone pair to the destination telephone pair for the duration of the call. During the conversation, voice signals are transmitted as over the connected pairs of wires. When the user hangs up the telephone receiver, then the switching equipment terminates the connection between the two pair of wires.
The above scenario applies, however, only to the interconnection of telephones within a local exchange. There are, in fact, hundreds of thousands of local exchanges all over the world. And to support the switching of calls from telephones in a source exchange to a destination exchange, there also exists a network of cables and supporting equipment. A cable or other medium that interconnects telephone exchanges, or telecommunications switches, is referred to as a trunk. A trunk typically is specified to support an average number of calls between its source telecommunications switch and destination telecommunications switch. Hence, when a call is placed from a source telephone interfaced to the source switch to a destination telephone interfaced to the destination switch, the switching equipment in both the source exchange and the destination exchange interact to effect the call. The source telecommunications switch decodes the called number and switches, or routes, the call over one of the trunks connected to the destination exchange. The destination telecommunications switch receives the call over the trunk from the source exchange, and further decodes the called number so that the call is routed to the destination telephone. In any metropolitan area today, there is network of local telephone exchanges along with their associated inter-exchange trunks to handle the switching of calls made within that area.
Similarly, these larger, metropolitan networks of exchanges are interconnected together in the same manner: A series of trunks interconnect all of the metropolitan areas within the United States and likewise, trunks interconnect most of the countries of the world. A trunk is the primary interconnection media for the PSTN.
In earlier years, as noted above, trunks essentially consisted of some number of wires between two central office switches. But in addition to the wires, trunks also consisted of a number of in-line signal amplifiers to prevent degradation of the analog voice signals that were routed over the interconnecting trunks.
In the 1960""s, a major development within the telecommunications industry enabled service providers to improve the quality of trunk interconnections, while at the same time drastically reducing the number of wires which were theretofore required to provide trunk interconnections between central office switches. This development, the T1 carrier protocol, prescribes a series of time-division multiplexed formats for the transmission of digitized telephone conversation data, each of which allow up to 24 separate conversations to be carried between switches on the same pair of telephone wires. A basic T1 signal is a pulse coded modulation carrying 24 8-bit data elements, each of the 8-bit data elements containing a digitized and encoded sample of one of the 24 conversations. Samples are taken from each of the 24 conversations, or channels, at a rate of 8,000 samples per second and these samples are continuously transmitted at a 1.544 Mbps carrier frequency over a single pair of wires. A 125-microsecond portion of the transmission that contains encoded samples from channels 1 through 24 is known as a T1 frame. In actual practice, out-of-band signaling bits and other information are also contained in a T1 frame, however, the basic structure of a T1 frame is as described above.
The T1 carrier protocol is the basis protocol that is used to transmit trunk data within the United States. Today, it is more common to find high speed inter-exchange trunk links such as T3 links or OC-48 links. These links are, however, aggregates of T1 links that are generated by combining T1 link signals through devices commonly referred to as add drop multiplexers (ADMs). In Europe, the basis protocol used for trunks is E1. The E1 protocol varies from the U.S. standard in terms of the encoding of the signals, in terms of the number of channels that are sampled and transmitted at the 8,000 sample/second rate, and in the absence of signaling bit information. In E1, there are 32 channels per frame rather than 24. To achieve the 8,000 sample/second rate, the E1 carrier is transmitted at 2.048 Mbps. In Europe, ADMs are also used to aggregate E1 links into higher speed trunks such as E3 trunks.
The benefits provided by the T1(E1) protocol caused a significant expansion in the services provided over the. PSTN. As a result, telephone service providers have invested substantially in switching equipment that provides trunk signals compatible with the T1(E1) protocol. It is virtually impossible today to find a telecommunications switch which does not employ some form of the T1 protocol for the provision of inter-switch trunks. And service providers have continued to increase their investment in T1 switching technologies for nearly forty years. As alluded to above, a typical present day trunk consists of a number of aggregated T1 links, the most common form adhering to OC-48 protocol. OC-48 prescribes a 2.5 Gbps transmission rate.
Two developments during the 1980""s, however, began to push the telecommunications industry to provide expanded and more varied services, i.e., services other than the transmission of voice signals. Advances in microcircuit design and fabrication techniques have enabled a significant percentage of the civilized world to have a computer in the home or office. In conjunction, advances in computer networking techniques and protocols have enabled all of those computers to communicate over the Internet. The Internet is a global network of interconnected computers that utilize a packet-switched communications protocol known as Internet Protocol (IP). And since the cables and trunks within the PSTN already provided the initial skeletal structure for integrating local, metropolitan, and global networks of computers, telephone service providers began to provide, and continue to provide, routing and distribution services for computer data that is transmitted via the Internet.
Five years ago, approximately 95 percent of the traffic passed over the PSTN was voice traffic. Today, voice traffic accounts for only 50 percent; computer data accounts for the remaining 50 percent of the traffic. And projections indicate that within another five years, computer data will account for over 90 percent of the traffic that is transmitted. Telephone service providers are now just beginning to significantly invest in packet-switched equipment for routing of computer data, or IP data.
The definite trend, both in terms of use and advances, is away from conventional synchronous networks based upon the T1(E1) protocol, and towards very high speed packet-switched networks. Consequently, present day telephone service providers are beginning to provide packet-switched network routers for the routing of computer data in collocation with their central office switching equipment. In such an arrangement, the central office T1(E1) switching equipment provides for the transmission of telecommunications signals over the T1-based network and the packet-switched equipment is used to route computer data over high bandwidth data networks. And while a number of developments have allowed packet-switched data to be transmitted over T1 trunks in the form of T1 frames, there is no extant system that allows T1 protocol frames to be transmitted over a packet-switched IP network. Granted, techniques and equipment exist for the transmission of voice-type signals over packet-switched networks, but these techniques require the complete replacement of T1 equipment within a PSTN switch with voice-over-IP (VOIP) equipment. Because of their substantial investment in T1(E1) switching equipment, telephone service providers are reluctant to make the change to VOIP.
Yet service providers are still pressed to increase telecommunications capacity through the addition of trunks between their telecommunications exchanges. But because they are quite reluctant to abandon their substantial investment in existing T1(E1) switching equipment, they consistently choose to add trunks that employ T1(E1)-based network equipment. The choice to utilize T1(E1) equipment is relatively expensive when compared to utilizing packet-switched network equipment. And in addition, the choice is short-sighted due to the fact that the industry is moving toward the increased use of packet-switched networks.
Therefore, what is needed is an apparatus that allows service providers to add T1(E1) trunks between central office switches that takes advantage of high speed packet-switched data networks.
In addition what is needed is a T1(E1)-to-IP multiplexing system that interfaces to T1(E1) telecommunications switching equipment but effects a T1(E1) carrier link over a high bandwidth data network.
Furthermore, what is needed is a method for sending T1(E1) signals between T1(E1) switches that utilizes a packet-switched network to deliver T1 frames to their intended destination.
To address the above-detailed deficiencies, it is an object of the present invention to provide an apparatus for implementing a T1(E1) trunk between two central office switches that utilizes a packet-switched data network as the transmission medium.
Accordingly, in the attainment of the aforementioned object, it is a feature of the present invention to provide a multiplexer, for transmitting/receiving central office switch communications from/to a first central office switch to/from a second central office switch, the multiplexer utilizing a high bandwidth data network for communicating. The multiplexer includes trunk interface logic and network translation logic. The trunk interface logic is coupled to the first central office switch via a central office switch trunk, and receives/transmits the central office switch communications from/to the first central office switch. The network translation logic is coupled to the trunk interface logic. The network translation logic translates the central office switch communications to/from data network communications, so that the central office switch communications may be transferred over the high bandwidth data network to/from the second central office switch, thereby providing all channels of the central office switch trunk between the first and second central office switches.
An advantage of the present invention is that telephone service providers can utilize packet-switched technology to implement a T1(E1) trunk without having to change out their existing T1(E1) central office switches.
Another object of the present invention is to provide T1(E1)-to-IP multiplexer that interfaces to a TI(E1) central office switch but implements a T1(E1) carrier link over a high bandwidth data network.
In another aspect, it is a feature of the present invention to provide an apparatus for transmitting telecommunications frames between telecommunications switches via a high bandwidth data network. The apparatus has a plurality of telecommunications interface ports, network translation logic, and a network interface port. The plurality of telecommunications interface ports are each configured to transmit and receive frames associated with a corresponding telecommunications trunk, where the corresponding telecommunications trunk interconnect two of the telecommunications switches. The network translation logic is coupled to the plurality of telecommunications interface ports. The network translation logic translates outgoing frames into outgoing data packets for transmission over the high bandwidth data network, and translates incoming data packets into incoming frames for distribution to the plurality of telecommunications interface ports. The network interface port is coupled to the network translation logic. The network interface port provides full-duplex routing of the outgoing data packets and the incoming data packets over the high bandwidth data network, where the full-duplex routing enables all channels of the corresponding telecommunications trunk to interoperate between the telecommunications switches.
In a further aspect, it is a feature of the present invention to provide a telecommunications carrier multiplexer, for providing trunk signals between telecommunications switches, where the trunk signals are transmitted over a packet-switched data network. The telecommunications carrier multiplexer includes trunk interface logic, network translation logic, and network interface logic. The trunk interface logic transmits and receives trunk frames corresponding to a particular telecommunications trunk, where the particular trunk interconnects a first telecommunications switch and a second telecommunications switch. The network translation logic is coupled to the trunk interface logic and translates the trunk frames associated with the first and second telecommunications switches into network packets for transmission over the high bandwidth data network. The network translation logic has application envelope logic that appends a corresponding application header to each of the trunk frames to form a plurality of application packets, where the corresponding application header provides control data that enables transmission of a corresponding trunk frame. The network interface logic is coupled to the network translation logic and provides full-duplex routing of the network packets over the data network. Each of the network packets has an application packet set, comprising those of the application packets that are generated during a 250-microsecond interval. Each of the network packets also has an IP header, appended to the application packet set to form an IP datagram, that provides IP network routing information for the application packet set.
In yet another aspect, it is a feature of the present invention to provide a telecommunications switch interconnection apparatus. The telecommunications switch interconnection apparatus includes a trunk frame multiplexer and a data network router. The trunk frame multiplexer receives trunk frames from a source central office switch, and translates the trunk frames into network packets. The data network router is coupled to the trunk frame multiplexer. The data network router transmits the network packets over a high speed data network, where the network packets are transmitted in such a manner as to effect transmission of the trunk frames from the source central office switch to a destination central office switch.
Another advantage of the present invention is that telephone service providers can employ unused bandwidth on their packet-switched networks to carry T1 (E1) trunk data. Yet a further object of the present invention is to provide a method for sending T1(E1) signals between T1(E1) switches that utilizes a packet-switched network to deliver T1 frames to their intended destination.
In yet a further aspect, it is a feature of the present invention to provide a method for interconnecting central office switches via a high bandwidth data network. The method includes receiving telecommunications frames from a source central office switch for delivery to a destination central office switch, translating the telecommunications frames into a plurality of network data packets and transmitting the plurality of network data packets over the high bandwidth data network, and converting the plurality of network data packets back into the telecommunications frames and providing the telecommunication frames to the destination central office switch.
Yet a further advantage of the present invention is that multiple T1(E1) trunks can be added between a number of central office switches over the same packet-switched network medium.